In recent years, eye diseases such as cataracts are often treated with an operation that replaces the affected crystalline lens in the eye with an intraocular lens (an artificial crystalline lens). Phacoemulsification and aspiration (PEA) is widely employed in such a surgical operation wherein the affected crystalline lens is pulverized and emulsified using ultrasonic vibration and then the pulverized part is aspirated. In this surgical operation, an apparatus such as, for example, that shown in FIG. 16 is used. This apparatus is constructed so that a supply tube 51 for introducing a perfusate into the anterior chamber S of the affected part of the eye is connected to an ultrasonic handpiece 53, which is an apparatus for use in PEA (hereafter, this apparatus may be simply called a “handpiece”). The handpiece 53 is provided with an inlet channel 54 (see FIG. 17) for introducing the perfusate to the affected part, and the supply tube 51 is connected to the rear end of the inlet channel 54. A perfusate bottle 55 holding the perfusate is connected to the supply tube 51. By placing the perfusate bottle 55 at a predetermined height, it is possible to supply the perfusate into the anterior chamber S by allowing it to drip freely by its own weight from the perfusate bottle 55.
In a surgical operation, a crystalline lens P is pulverized and emulsified by ultrasonic vibration while supplying the perfusate into the anterior chamber S. The emulsified crystalline lens is aspirated and discharged together with the perfusate by an aspiration pump 59 that is connected to an aspiration channel 57 (see FIG. 17) provided in the handpiece 53. The anterior chamber is kept stable by the stable balance between the inflow rate (inflow pressure) of the perfusate and the aspiration rate (aspiration pressure).
However, this apparatus has the following problems. Generally, the PEA conducted in a cataract operation is performed in such a manner that fragments of the lens nucleus P1 are drawn to the tip entrance as shown in FIG. 17, and the fragments are then emulsified and aspirated by ultrasonic vibration using a dribble effect. At this time, the tip entrance is blocked by the lens nucleus P1, and the inflow of the perfusate is stopped while the tip entrance is blocked. When aspiration is further conducted under this condition, negative pressure builds up in the aspiration channel 57 and the lens nucleus P1 is aspirated. The obstructive state of the aspiration channel 57 is thereby cleared, and at that moment, the instantaneous aspiration rate rapidly increases and the inside of the anterior chamber S becomes decompressed. However, because it is impossible to control the supply of the perfusate instantaneously to cope with this decompressed state, a condition continues wherein the amount of perfusate aspirated into the aspiration channel 57 is greater than that supplied from the supply tube 51. This adversely affects the balance between the inflow rate (pressure) and aspiration rate (pressure) of the perfusate, and the anterior chamber becomes unstable. As a result, the decompressed condition in the anterior chamber S continues (hereunder, this is called a “surge”) until the inflow of the perfusate that was previously stopped reaches a certain rate and the inflow pressure and aspiration pressure eventually achieve a state of equilibrium. This causes a so-called microcollapse in which the internal capacity of the eyeball and anterior chamber decreases, which may cause further destruction of the posterior chamber and damage to the corneal endothelium.
Conventionally, operators coped with this problem by suitably selecting the amount of ultrasonic waves and aspiration amount based on their actual experience and/or practice. Therefore, it was not easy for inexperienced surgeons to cope with this problem.
To reduce such a surge, WO97/37700, for example, discloses an apparatus for detecting the blockage in an aspiration line using a vacuum sensor provided in the aspiration line. This apparatus is designed so that, when a blockage in the aspiration line is detected, the rate of the perfusate flowing into the eye is changed by controlling the speed of the peristaltic pump with a computer. U.S. Published Application No. 2002/0019607 and Japanese Unexamined Patent Publication No. 2002-153499 disclose an apparatus comprising an irrigation reservoir for storing irrigation fluid, a range, an irrigation pressure sensor and a pressure controller provided at a point midway along the irrigation line. This apparatus prevents the internal pressure of the anterior chamber from dropping below a specified value by using the controller to operate the irrigation reservoir in such a manner that an irrigation fluid is forcibly supplied to an irrigation supply channel when the irrigation pressure exceeds an appropriate range.
However, because the surge occurs instantaneously for a short time of less than about 0.2 second, it is difficult in practical terms to suppress the surge without any time lag using these apparatuses.
U.S. Pat. No. 6,042,586 discloses an apparatus which is connected to an irrigation supply line for preventing a cornea from collapsing. This apparatus comprises a main body provided with a dome-shaped head having a through bore and a thin latex film having a fixed periphery attached to this head so as to block this through bore. Because the thin film is elastic, when the irrigation flows to the thin film side via the through bore, the thin film stretches so as to form a chamber between the film and the head.
EP Patent No. 0180317 and U.S. Pat. No. 4,841,984 disclose that a pressure chamber is connected in series or in parallel to an irrigation fluid tube. This pressure chamber is formed into a spherical shape having an elastic surface. They state that it is preferable that the sphere have a diameter of 4 to 8 cm and be disposed 6 to 10 cm from a needle tip. It is also disclosed that by filling the chamber with air or other gas from the beginning, the time for responding to the change in intraocular pressure can be shortened.
However, because in intraocular operations such as cataract surgery, very precise and delicate manipulation is required, if the chamber is located at a position 6 to 10 cm from the tip of the handpiece as mentioned above, the motion of the hands operating the handpiece is restricted and this interferes with the surgery. During the surgery, the handpiece may be rotated around its axis or pivoted around its tip to aspirate the nucleus, and when the handpiece moves, the chamber also moves with it. This may cause the airspace in the chamber to move toward the irrigation inflow hole (the portion connected to the irrigation inflow line). This not only prevents the irrigation fluid from being promptly supplied but also raises the possibility that air may flow into the eyeball, which may cause additional damage to the intraocular tissues that is different from that caused by the surge.
Furthermore, because it is difficult to mount the chamber near the handpiece, depending on the motion of the chamber, the irrigation supply tube that composes the irrigation supply line may be strongly twisted. This would prevent the irrigation fluid from being supplied to the eye and may cause the anterior chamber to collapse due to strong aspiration pressure and lead to a serious accident.
Japanese Unexamined Patent Publication No. 1998-43229 discloses an apparatus comprising a perfusate reservoir means which stores perfusate, and has an air chamber disposed in the pathway of a perfusion tube. However, this publication discloses that it is preferable that the perfusate reservoir be located near the handpiece, and this may cause the same kind of problem as described above for the chamber.
The publication also discloses the steps of supplying the perfusate into the perfusate reservoir means as follows: A piston provided in the perfusate reservoir means is pressed down to exhaust the air in the perfusate reservoir means via an air inlet hole in an infusion tube that is connected to the perfusion tube. When the piston returns to its original position due to hysteresis, perfusate in an amount equal to the capacity occupied by the transferred piston is aspirated into the perfusate reservoir means from the perfusion bottle. The present inventor and associates produced the same apparatus as the above-mentioned perfusate reservoir, and examined the effect. When they tried to discharge the air in the perfusate reservoir by pressing the piston, not only could the air not be discharged from the air inlet hole but the piston could not even be pushed down. Therefore, the present inventor and associates verified that a perfusate cannot be supplied using the above-described perfusate reservoir. It is assumed that this is because the air inlet hole of commonly used infusion tubes is communicably connected to the perfusion bottle to keep the pressure in the perfusion bottle stable, and the perfusate reservoir is structured so as to prevent the perfusate and/or air from leaking outside via the air inlet hole.
The present inventor proposed an intraocular surgical apparatus comprising a decompression-compensating instrument as disclosed in Japanese Unexamined Patent Publication No. 2001-170102 (corresponding U.S. patent Publication No. 2002/0095113A1). As shown in FIG. 18, this intraocular surgical apparatus comprises a tube 63 (whose inner diameter is the same as that of a supply tube 51) having a plug 61 on one end, the tube 63 serving as a storage member for the decompression-compensating instrument and being connected to the supply tube 51 at a midpoint thereof. This intraocular surgical apparatus is used in the following manner. The end of the handpiece is first inserted in the anterior chamber S to start a the surgery. At this moment, the internal pressure (or capacity) of the anterior chamber S, which is the intraocular pressure, is kept stable by the balance between the inflow rate (inflow pressure) of the perfusate and the aspiration rate (aspiration pressure). During the surgery, when the balance between the inflow rate (inflow pressure) of the perfusate flowing into the anterior chamber S and the aspiration rate (aspiration pressure) is stably maintained and the emulsified crystalline lens is smoothly discharged, the air in the tube 63 is compressed between A-B as shown in FIG. 18. When the aspiration channel 57 is blocked by fragments of the lens nucleus, the inflow pressure of the perfusate affects the anterior chamber S. The air between A-B is further compressed so as to have the same pressure as the anterior chamber S, and the air capacity is reduced to that between A-C as shown in FIG. 19. In other words, the perfusate flows in the tube 63 in the amount equivalent to the capacity between B-C, which corresponds to the capacity of the air compressed. Although the aspiration pump 59 keeps aspirating the perfusate, the amount of perfusate in the aspiration channel gradually decreases because of the blockage thereof, resulting in a rapid increase of the negative pressure in the aspiration channel. When the fragment of the lens nucleus that was blocking the aspiration channel 57 is aspirated, the negative pressure is rapidly transferred to the anterior chamber S and then to the tube 63. Following the rapid decrease of the pressure in the anterior chamber S, the air between A-C in the tube 63 expands to the area between A-D as shown in FIG. 20. This pushes the perfusate stored between C-D out, wherein it flows to the anterior chamber S. This alleviates the rapid decrease of the pressure in the anterior chamber S and the stable balance between the inflow rate of the perfusate and the aspiration rate is maintained, preventing microcollapse.
Subsequently, the present inventor conducted extensive research to improve the above invention and found that when a tube serving as a storage member of a decompression-compensating instrument is disposed on the handpiece, from the moment that the surge occurs until it returns to a normal perfusion condition, the perfusate does not flow to the anterior chamber at a stable rate depending on the capacity or inner diameter of the tube. As described above, if the surge occurs when the tube is disposed thereon, the perfusate flows from the tube into the anterior chamber in accordance with the decompressed condition of the anterior chamber, but thereafter the perfusate flows to the anterior chamber via the supply tube as usual. However, depending on the capacity of the tube, etc., when the inflow of the perfusate changes from the tube to the supply tube, the inflow does not switch smoothly. When such a phenomenon occurs, the inflow of the perfusate to the anterior chamber sometimes cannot adequately cope with the surge and the decrease of the pressure in the anterior chamber may not be reliably alleviated.
An object of the present invention therefore is to provide a decompression-compensating instrument that reliably prevents the affected part in the eye from being rapidly decompressed during surgery for treatment of cataracts, etc., a surgical apparatus equipped with this instrument for use in intraocular surgery, and a method for conducting surgery using the same.